The processing of biological fluid such as blood or blood components may involve using a reusable processing apparatus (“hardware”) and a disposable fluid circuit adapted for mounting or other association with the reusable apparatus. The fluid circuit typically includes containers such as plastic bags and associated tubing that defines a flow path through the circuit. The disposable fluid circuit may also include one or more separation devices where the biological fluid/cells can be separated into two or more components, washed or otherwise processed. Separation devices may separate the biological fluid based on centrifugal separation and/or, as described below, membrane separation.